Who crews the boats?

[Inziladun]

Tuor in Gondolin

How did Bilbo, Frodo, and Gimli return to Middle-earth-who
piloted the ships? (I believe they did return since (especially
Frodo) they were there for a period of healing-not permanent
residence)?

I don't think they ever came back from Eressëa. The mortals who went there were indeed only there temporarily, but there is no description in the books that I am aware of that says they were allowed to return to ME. At the end of their natural lives they would simply die.